In a prior-art process for the cooling of articles or objects with low-temperature gases, especially materials which at their transformation temperatures cannot be comminuted readily or are difficult to comminute, a deep-cooled cold gas at low temperatures is brought into contact with the materials to embrittle them. Directly upon such cooling, the materials may be introduced into a comminuting unit which may employ jet mills, pin mills, abrasion mills, impact mills or other comminuting elements to finely divide the materials. Such materials include plastics (synthetic resins) which are relatively soft at room temperature and which are not readily comminuted to a powder. By the use of deep-cooling processes, such materials can be embrittled to the point that the subsequent milling is capable of breaking up the material or articles and forming a powder therefrom. As the cooling gas, nitrogen has been used most frequently and is often sprayed in a liquid state into the cooling zone.
While such cooling processes have been found to be relatively satisfactory as far as the embrittlement of the materials goes, it has been found recently that the operation of the apparatus for carrying out the cooling involves several difficulties in certain cases. One of these difficulties resides in that the requirements for the liquefied cooling gas differ in accordance with the materials and volumes thereof passed through the apparatus, the nature of the materials, the temperatures and the temperatures to which they must be reduced in order to obtain embrittlement. The apparatus and the liquefied gas supplied is usually dimensioned for the peak requirements and hence the operation becomes uneconomical when for certain temperature ranges the cooling is carried out with liquefied gas exclusively.